1. Field of the Invention
The present invention relates to a projection display device for enlarging and displaying an image on an imager onto a projection plane, and more particularly to a projection display device of a type for projecting projection light onto a projection plane in an oblique direction.
2. Description of the Related Art
Currently, a projection display device (hereinafter, called as a “projector”) of a type for enlarging and projecting an image on an imager (such as a liquid crystal panel) onto a projection plane (such as a screen) has been commercialized and widely used. In the projector of this type, various methods have been proposed to reduce the throw distance. The “throw distance” is a distance from a projection opening of a projector or a most downstream optical component of a projection optical system to a flat plane including a projection plane. If the throw distance is reduced, for instance, projection light is less likely to be blocked by an obstacle, thereby increasing the operability of a projector, and usability for a user.
As a method for reducing the throw distance, there is proposed an arrangement of increasing the view angle of a projection optical system, and tilting the propagating direction of projection light with respect to an optical axis of the projection optical system. For instance, a wide angle lens having a large view angle is used as a projection optical system, and an imager and a screen are displaced in directions opposite to each other with respect to an optical axis of the projection optical system. This enables to reduce the throw distance.
As another arrangement, a refractive optical system and a reflection optical system are used as a projection optical system. In this arrangement, an image on an imager is formed between the refractive optical system and the reflection optical system, as an intermediate image. The intermediate image is enlarged and projected onto a screen in an oblique direction by the reflection optical system (a curved surface mirror). This enables to reduce the throw distance.
In the projector of oblique projection type, the size of a projected image (hereinafter, called as a “projection size”) can be adjusted by changing the throw distance, as necessary. For instance, reducing the throw distance by disposing a projector main body closer to a screen enables to reduce the projection size. Further, increasing the throw distance by disposing the projector main body away from the screen enables to increase the projection size.
In the arrangement of projecting projection light with a wide view angle and in an oblique direction, if the throw distance is changed, the position of a projected image may be greatly displaced vertically on a projection plane depending on a change in the throw distance. In view of this, in the case where the projection size should be changed during a projecting operation, it is necessary to quickly correct the position of a projected image, depending on a change in the throw distance to change the projection size.
In view of the above, there is proposed an arrangement provided with a shift mechanism for moving an imager in a vertical direction with respect to an optical axis of a projection optical system to adjust the position of a projected image. Use of the shift mechanism enables to easily adjust the position of a projected image, without the need of moving a projector itself to adjust the position of a projected image.
In a projector, it is necessary to accurately position an effective display surface of an imager with respect to an object plane of a projection optical system. If the effective display surface is displaced from the object plane, a projected image may be blurred. In particular, in the projector of oblique projection type as described above, a small displacement of the effective display surface with respect to the object plane causes a blur in a projected image. In view of this, it is necessary to strictly adjust the distance between a projection optical system and an imager (the effective display surface) in the projector of oblique projection type.
As shown in FIG. 14B, an effective display surface may be displaced with respect to an object plane, if the effective display surface is tilted with respect to the object plane. If the effective display surface is tilted with respect to the object plane, a displacement amount between an end portion of the effective display surface and the object plane in the tilted direction is increased. As a result, a projected image in an area corresponding to the end portion where the displacement amount is large may be greatly blurred.
Further, if the imager is shifted in a state that the effective display surface is tilted as described above, as shown in FIG. 14C, the displacement between the end portion of the effective display surface and the object plane is further increased. As a result, the projected image is increasingly blurred.
As described above, in the arrangement of shifting an imager, the positional relation between the imager and the projection optical system is required to be properly maintained, while shifting the imager. Thus, there is a demand for a method for mounting an imager and a projection optical system in a projector with high precision.